A basic and conceptual question from arithmetic progression chapter in we have been asked to find the sum of (−5)+(−8)+(−11)+.....+(−230).
RS Aggarwal, Class 10, chapter 5C, question no 2(iii).
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It is an A.P.,
in which, a=−5,d=−8−(−5)=−3,l=−230
First calculate the number in series…..
l=a+(n−1)d
−230=−5+(n−1)−3
−225=−3n+3
3n=228
n=76.
Now,
Sum of the series =n/2(a+l)
76/2(−5−230)
38×−235=−8930.
So, the sum of your series would be −8930.